1. Field of the Invention
The present invention relates to a heat-storage unit capable of storing heat such as waste heat and transporting heat to a remote place, and an operation method of the heat-storage unit.
2. Description of the Prior Art
Heat generated from a factory such as ironworks and garbage-disposal facility, for example, is used in various facilities near the factory. Further, by temporarily storing the heat generated from the factory in a heat-storage material or the like and transporting the heat-storage material, the heat can be used in a place remote from the factory. As an apparatus for storing heat, there exists an apparatus that performs heat exchange by directly contacting a medium such as oil, to which heat was supplied, with metal hydrate and stores heat into the metal hydrate.
For example, the storage container of International Publication No. WO 03/019099 houses a heat-storage material such as sodium acetate that stores heat and oil having a smaller specific gravity than that of the heat-storage material. Since the specific gravity of oil is smaller and oil and heat-storage material do not mix with each other, they are housed in a vertically separated manner. Then, pipes are disposed in the oil and the heat-storage material and are severally connected to a heat exchanger. Oil is taken into the heat exchanger from one pipe, heat is supplied to the oil, and the oil to which heat was supplied is discharged from the other pipe. Since the discharged oil has small specific gravity, it goes up to oil in the upper portion. Heat is exchanged by the direct contact between the heat-storage material and the oil as the oil goes up. By repeating the above-described action, heat is stored in the heat-storage material. Then, the pipes of International Publication No. WO 03/019099 are in a double pipe structure in order to prevent impurities from entering the pipes and the heat exchanger.
Further, in the storage container of International Publication No. WO 03/019099, when taking out the heat stored in the heat-storage material, oil to which heat is not supplied is discharged from the pipe arranged in the heat-storage material. Then, while the oil goes up to the oil in the upper portion, the stored heat is supplied to the ascending oil by the direct contact between the heat-storage body and the oil. By taking out heat in the heat exchanger from the oil to which heat was supplied, the stored heat can be used. By repeating the above-described action, the heat stored in the heat-storage material can be taken out (heat radiation of heat-storage material).
A heat-storage material such as sodium acetate that stores heat utilizes latent heat of fusion, its state changes from solid to liquid as heat is added and heat is stored in the heat-storage material, and the state changes from liquid to solid as heat is taken out to radiate heat from the heat-storage material. For this reason, because the heat-storage material at the starting point of heat storage is solid in International Publication No. WO 03/019099, discharge holes are clogged by the solid heat-storage material even when the storage container tries to discharge the oil, to which heat was supplied, from the pipe arranged in the heat-storage material, the oil cannot be discharged until heat is added to the heat-storage material and the material changes to liquid, and there are cases where the pipe bursts.
To solve the problem, a constitution is considered where another pipe is provided for letting out the oil in the pipe arranged in the heat-storage material until the heat-storage material melts and the oil can be discharged from the discharge holes. However, in taking out the stored heat in this constitution, the flow path resistance of the discharge holes becomes larger as the state of the heat-storage material reversely changes from liquid to solid, so that the oil in the pipe is not discharged from the discharge holes into the heat-storage material but flows to the pipe, which was provided separately, as heat is radiated from the heat-storage material. Consequently, it becomes impossible to directly contact the heat-storage material with the oil, and heat cannot be sufficiently taken out from the heat-storage material.